The names of the months apparently originated somewhere slightly farther north than most Ethsharites live and they do not precisely match the actual weather conditions in the Hegemony. Also, the length of day varies relatively little, so even at the winter solstice the nights are only slightly over thirteen hours.
Each month is thirty days long, originally set to match the cycle of the larger moon. Between years there is a festival (called Festival) which starts on the vernal equinox and lasts five or six days. At the end of the Great War, there was a seven day Festival. Presented as a celebration of the conclusion of hostilities several scholars have noted that the calendar had gotten a bit off due to preoccupation during the War. Including this inter-year Festival there are roughly 365 days between new years. Because of the various Festivals the cycle of the larger moon is no longer syched to the month as was originally intended.
Days are also grouped into sixnights, lasting six days (or nights) apiece. The individual days do not have names and are simply numbered. Occasionally someone will count a twelvenight, which is simply 2 sixnights or 12 days.
There are 5 sixnights to a month and 60 sixnights to a year, not including Festival.